The present invention relates generally to a radar system and a method of generating waveforms for use by the radar system. More particularly, the present invention relates to an impulse radar system that generates individual pulses of a pulsed waveform from spectral components having frequencies that vary between individual pulses.
Radar systems generally require bandwidth in order to resolve targets, i.e., the larger the bandwidth, the higher the range resolution. Conventional radar systems use waveforms with long pulse width and typically have an instantaneous bandwidth on the order of 100 MHz. To improve the instantaneous bandwidth, exploration has been done in connection with impulse radars. Impulse radars use a train of short pulses on the order of 200 picoseconds and have been shown to have an instantaneous bandwidth on the order of 5 GHz.
In the past, impulse radars have taken the approach of switching the RF transmit signal on and off in picoseconds in order to generate the train of extremely short pulses. However, such systems generally require the impulse generator to have a peak power on the order of several megawatts due to the fact that it has a low duty factor in that the pulse width of the impulse generator is extremely short when compared to the required interpulse period.
In an effort to ameliorate these problems, the inventor of the present invention explored an ultra-wide bandwidth radar that used a specified set of narrow band spectral components to synthesize a waveform with very high range resolution. This concept, which was embodied in U.S. Pat. No. 5,146,616 (the ""616 patent) and U. S. Pat. No. 5,239,309 (the ""309 patent), was implemented by combining (summing) multiple continuous wave sources having frequencies that were equally spaced. This superposition of continuous wave sources resulted in the desired repeating pulse train without the need for fast switching circuits. However, the waveform described in the aforementioned patents required that the transmitted sources be evenly spaced across at least a portion of the available frequency spectrum.
Recently, a need has been expressed for a radar system that could operate in the communication bands, e.g., from 3 Mhz to 1 GHz (covering HF, VHF, and UHF bands). Such a radar would be quite useful, particularly since it would have superior foliage penetration to radars operating at microwave frequencies and above. Unfortunately, the impulse radars of the prior art, including those covered by the ""616 patent and the ""309 patent, would not be suitable for such operation. Specifically, the prior art impulse radar systems are likely to interfere with communication signals being transmitted in the band of operation of the radar.
Therefore, it would be advantageous to have a radar system that could operate in the communication bands without interfering with other users transmitting within these bands.
The present invention provides a radar system that uses a wide bandwidth pulsed signal that is composed of spectral components having frequencies spaced at irregular intervals. Specifically, the present invention provides a radar system that is capable of varying the frequencies of the spectral components composing individual pulses of the pulsed signal so as to avoid interfering with ongoing communications within the radar""s transmission band.
In accordance with one aspect of the present invention, a radar for locating and tracking objects based on the use of a pulsed waveform, each pulse of the pulsed waveform being made up of a plurality of spectral components having different frequencies is provided. The radar includes an antenna and a transmitter operatively coupled to the antenna for generating the plurality of spectral components that make up each pulse of the pulsed waveform. The radar further includes a receiver operatively coupled to the antenna for receiving signals at the frequencies of the plurality of spectral components and a signal processor operatively coupled to the receiver for processing the received signals in order to generate and output a radar presentation and to detect the presence of other signals at particular frequencies. The signal processor is operatively coupled to a display for displaying the radar presentation. Finally, the radar includes a controller operatively coupled to the transmitter and the signal processor for varying the frequencies at which the plurality of spectral components are generated, such that the transmitter generates spectral components at frequencies different from the frequencies of other signals detected by the signal processor.
In accordance with another aspect of the present invention, a radar is provided wherein the controller suppresses the generation of those spectral components having frequencies that are the same as the frequencies of the other signals detected by the signal processor.
In accordance with still another aspect of the present invention, a radar is provided wherein the spectral components are produced at frequencies within a frequency band of between approximately 20 MHz and approximately 600 MHz.
In accordance with still a further aspect of the present invention, a method of generating a pulsed waveform having a plurality of spectral components is provided. The method includes the steps of listening across a predetermined frequency band in order to determine which frequencies within the frequency band are available for transmission and generating for a finite period of time a plurality of spectral components having frequencies corresponding to at least a portion of the frequencies available for transmission. The method further includes the steps of combining the plurality of spectral components into a pulse of the pulsed waveform, transmitting the pulse of the pulsed waveform, and repeating the prior steps to generate and transmit a plurality of subsequent pulses of the pulsed waveform.